This invention relates to a computer-based video/graphics memory system, namely method and apparatus.
As is well known, one form of computer memory is random access memory (RAM). This is in integrated circuit form, and may take the form of dynamic RAM or DRAM, or static RAM or SRAM. All types of RAM have a port through which random accesses to the memory locations may be made.
There is a need to use memory in a video/graphics or multi-processing applications. `Multi-media` is now becoming an important application of computer systems in which video signals at standard video line and field rates are intermixed for display with computer-generated graphics images. For display and for other purposes multiple sources and destinations of data need to have efficient and timely access to a common memory or storage device. It may be required to have simultaneous access to video, graphics and processed image data.
Conventional graphics sub-systems use dual-ported VRAM (video random access memory). The random access port is used by a host processor, or if present, a graphics processor, to create a graphics image by writing pixel values into a two-dimensional pixel array within the DRAM (dynamic RAM) core of the VRAM. A serial access port (SAM) is dedicated to reading out that data in raster line format, to refresh a cathode ray tube (CRT) display. The two ports, namely the normal random access port and the serial access port, function independently, except during transfers from the serial access port to DRAM core and vice versa.
There are problems in coordinating computer graphics and video signals in a single system. Our U.S. Pat. No. 5,027,212 describes one system for use in combining graphics and video information on a single display. Although extremely useful, there are limits on the capabilities of the system described in that patent.